The invention relates to a transmission drive arrangement with infinitely variable transmission ratio especially for automobiles in which one such infinitely variable transmission is used for transmitting drive power to each of the driven wheels.
The wheels of a car do not always rotate at the same speed. Differential speed of the curve inner and outer drive wheels is normally accommodated by a differential transmission which provides for each of a pair of driven wheels the same torque but permits rotation of the wheels at different speeds.
If each of a pair of drive wheels is driven separately by means of a pair of infinitely variable transmissions, for example of the type described in U.S. Pat. No. 3,810,398, there would be no need for a differential transmission if the transmission ratio of the two transmissions is controlled properly. A transmission and transmission ratio control arrangement in which the transmission ratio can be so controlled as to provide essentially the same torque for both of a pair of drive wheels is disclosed in U.S. Pat. No. 4,086,820. Such arrangements would be relatively inexpensive as the power is split and each of the two traction roller transmissions would be relatively small. A problem could occur with such an arrangement, however, when traction is lost at one wheel because the transmission ratio of the transmission for said one wheel would then rapidly change toward a greater ratio and the wheel speed would rapidly increase. When the wheel then arrives again at full traction the forces on the wheel and the respective transmission components are undesirably high.
It would therefore be desirable if such slipping could be avoided. Not only would excessive transmission load and wear be prevented but the chances of slipping on snow or mud would be reduced and driving safety could be improved.